Neotropical Ichthyology, 6(2):267-274, 2008 Copyright © 2008 Sociedade Brasileira de Ictiologia
Reef fish community structure on three islands of Itaipu, Southeast Brazil
José Policarpo de Mendonça-Neto, Cassiano Monteiro-Neto and Luiz Eduardo Moraes
We provide here the first assessment of the composition, abundance and distribution of rocky reef fishes of Itaipu Sound, Rio de Janeiro, off the southeastern Brazilian coast. Monthly visual censuses, benthic quadrats and chain link transects were conducted over one year on rocky reefs at three islands (Menina, Mãe and Pai). A total of 2466 individual fish, belonging to 29 families and 42 species were recorded. The most abundant fish species were Parablennius pilicornis, Haemulon steindachneri, Orthopristis ruber and Diplodus argenteus. Sheltered and complex habitats showed the most abundant and diverse fish populations. There was a major significant separation between sampling sites and a secondary seasonal pattern. The three sites showed similar fish communities with locally structured environmental gradients according to their inherent habitat characteristics. Apresentamos aqui o primeiro estudo da composição, abundância e distribuição de peixes recifais nos recifes rochosos da enseada de Itaipu, Rio de Janeiro, Brasil. Foram realizados mensalmente censos visuais, quadrats de composição bentônica e transectos com correntes durante um ano em recifes rochosos de três ilhas (Menina, Mãe e Pai). Um total de 2466 peixes pertencentes a 29 famílias e 42 espécies foi registrado. Os peixes mais abundantes foram Parablennius pilicornis, Haemulon steindachneri, Orthopristis ruber e Diplodus argenteus. Os recifes mais abrigados e com maior complexidade de hábitats foram os que apresentaram maior abundância e diversidade de espécies. Análises estatísticas revelaram distinções significativas entre as áreas amostradas e um padrão sazonal secundário. As três áreas apresentaram basicamente a mesma comunidade de peixes, estruturadas a partir de gradientes ambientais e de características estruturais próprias de cada ilha. Key words: Rocky reef fishes, Habitat complexity, Benthic biota. Introduction Most studies about the community ecology of Brazilian reef fishes began in the late 1990s, and applied underwater visual census techniques (Rosa & Moura, 1997; Rocha et al., 1998; Ferreira et al., 1998; Rocha & Rosa, 2001). These studies were conducted at several sites throughout the tropical and subtropical Brazilian coastline, from below the mouth of the Amazon River at the Manuel Luiz Reefs (0o52’ S) (Rocha & Rosa, 2001), to the south to Santa Catarina State (27o30’ S) (Floeter et al., 2001). On the southeastern Brazilian coastline, rocky shores comprise the habitat for reef fishes and other reef-associated biota (Floeter et al., 2004; Rangel et al., 2007). Despite an overall lower complexity when compared to coral reefs, rocky reefs are characterized by a high fish diversity and endemism (Ferreira et al., 2001; Rocha, 2003). Considering the continental dimension of the Brazilian coast (almost 8000 km), a limited set of scientific works on the ecology and community struc-
ture of reef fishes is currently available. Differences in reef fish communities can be found along geographic gradients (Parrish, 1989; Sale, 1991; Joyeux et al., 2001) and distinct reef types (Ebeling & Hixon, 1991; Ferreira et al., 2001; Bellwood & Wainwright, 2002). Patterns of occurrence and distribution of these assemblages often vary over space and time, influenced by a set of integrated physical and biological factors (McCormick, 1989; Syms & Jones, 2000; Acosta & Robertson, 2002). Wave exposure, water depth and topographic complexity may exert variable degrees of interference upon many ecological processes, such as recruitment, predation and territoriality (Caley, 1993; Cheney & Côté, 2003; Kawasaki et al., 2003). In this work, we analyzed reef fish community variation over space and time on three islands in Itaipu Sound, Rio de Janeiro, Brazil. We studied changes in species composition, abundance and diversity and their correlation with benthic coverage and habitat complexity.
Laboratório de Biologia do Nécton e Ecologia Pesqueira, Programa de Pós Graduação em Biologia Marinha, Departamento de Biologia Marinha, Universidade Federal Fluminense, Cx Postal 100644, 24001-970 Niterói, RJ, Brazil.
[email protected] (JPM)
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Reef fish community structure on three islands of Itaipu
Materials and Methods Study Site. This study was carried out on three islands of Itaipu Sound, Niterói, RJ, Brazil (22°58’S; 43°02’W) from April 2002 to March 2003. Menina Island, Mãe Island and Pai Island are, respectively, 1 km, 2.5 km and 4.2 km off the Brazilian coast. Pai Island is the farthest and most exposed study site. We selected one sampling station located on the sheltered face of each island (Fig. 1). This selection was based on water visibility and diving conditions which could enable surveys to be conducted throughout the year. Environmental variables and benthic biota. At each site, we measured water visibility (Secchi disk), water temperature at diving depth (°C, mercury thermometer) and site rugosity using the chain method (Luckhurst & Luckhurst, 1978) as an index of habitat complexity. Benthic organisms were pooled into ecological and morpho-functional groups: grazers (black and purple sea urchins), sessile constructive (mussels, oyster and barnacles), mobile (gastropoda, sea cucumbers and star fish) and sessile (anemones, turf algae and bryozoans). Individual counts and percent coverage were conducted on replicate 1-m² aluminum squares (quadrats) at different points within the same area where visual censuses for reef fishes were performed. Reef fish community. Reef fish community was assessed through 20 m x 2 m underwater strip transects (40 m2), varying from the shallowest zones to the bottom rocky/sand interface, about 6-9 meters deep. All sites were visited once a month, and censuses were conducted within the same day between 8:00 and 12:00, starting at Pai Island and finishing at Menina Island. We conducted a total of 108 transects, 36 on each site. Fish counts were conducted in a slow constant swimming velocity (Russ & Gladstone, 1990) and performed by the same observer (J. P. Mendonça-Neto). Sighted fishes were identified and counted,
and the information was recorded on a PVC plate (Williams, 1982). Afterwards, fish count data were expressed as frequency of occurrence and relative abundance. Statistical analysis. Renyi´s graphic ordination method was used to check if species diversity was comparable between sites (Hill, 1973; Legendre & Legendre, 1998). According to the method, when diversity patterns are parallel to each other, species diversity may be compared, but when diversity patterns cross each other, no comparisons are possible. Differences among average diversity were statistically tested with bootstrapping following the model proposed by Solow (1993). The Species Diversity & Richness v.2.3 software was used for all procedures (Henderson & Seaby, 1998). Multivariate analysis of the data including non-metric multidimensional scaling (nMDS) and analysis of similarities (ANOSIM) was performed with PRIMER 5 software (Primer-E 2000). Both procedures used a Bray–Curtis similarity matrix. MDS is a 3-dimensional ordination of samples brought down to a 2-dimensional plot. The quality of the plot is indicated by its stress value: values
